A component of many computers and data server systems is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider toward the surface of the disk, and when the disk rotates, air adjacent to the disk moves along with the surface of the disk. The slider flies over the surface of the disk on a cushion of this moving air. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic transitions to and reading magnetic transitions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head can include a magnetic write pole and a magnetic return pole, the write pole having a much smaller cross section at the ABS than the return pole. The magnetic write pole and return pole are magnetically connected with one another at a region removed from the ABS. An electrically conductive write coil is wrapped around the write pole and induces a magnetic flux that magnetizes the write pole when a current is passed through the coil. This results in a magnetic write field being, generated through the adjacent magnetic medium, the write field being substantially perpendicular to the surface of the medium (although it can be canted somewhat, such as by a trailing shield located near the write pole). The magnetic write field locally magnetizes the medium and then travels through the medium and returns to the write head at the location of the return pole where it is sufficiently spread out and weak that it does not erase previously recorded bits of data. The polarity of the write field is dictated by the polarity of the write current through the write coil. The polarity is switched based on a write clock whose frequency and phase are controlled to optimize the data write process.
A magnetoresistive sensor such as a GMR or TMR sensor can be employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, or barrier layer, sandwiched between first and second ferromagnetic layers, referred to as a pinned layer and a free layer. In a read mode, the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals.
In order to increase data density it is necessary to increase the track pitch, which means reducing the spacing, between data tracks. However, the spacing between data tracks has been limited by the size of the write pole of the write head. The amount by which the Write pole size can be reduced is limited by the need to provide sufficient magnetic write field to reliably write a hit of data to the magnetic media. One way to overcome this is to record data in a shingled fashion, wherein data tracks overlap one another. In such a system only the inner or out edge (depending on design) of the each of the data tracks is read. Such a system has shown promise for increasing data density, but has also presented challenges with regard to design, implementation and performance.